1. Field of the Invention
The present invention relates to an image forming apparatus used as a printer, and more particularly, to a lifespan management method for a plurality of components contained replaceably in an image forming apparatus.
2. Description of the Related Art
An image forming apparatus is a printing device, which performs printing by exposing an image to be printed onto an photosensitive drum, developing said image by adherence of toner, and then transferring the visible image to printing paper and fixing the image thereon. Moreover, in the case of color printing, the respective steps described above are carried out for four toners of different colors, namely, Y (yellow), M (magenta), C (cyan) and K (black).
The aforementioned exposure and developing steps are carried out by means of a print unit installed replaceably in the image forming apparatus. This print unit comprises a photosensitive drum, and the like, and hence is a consumable part. Therefore, the lifespan thereof is managed, and when it reaches the end of its lifespan, the print unit must be replaced. Moreover, similar lifespan management is necessary for other consumable parts (or components), such as toner cartridges contained inside the print unit, the fixing device and belts located outside the print unit, and the like.
Conventionally, the lifespan of a component, such as a print unit, is managed by means of lifespan management information, such as a lifespan print copy number or lifespan time period, or the like, for each component, stored in a non-volatile memory (for example, an EEPROM,) in the image forming apparatus. Thereupon, when the number of printed copies reaches the lifespan number of copies, or when the operating time reaches the lifespan time period, a replacement indicator is displayed on the operating panel of the image forming apparatus, thereby prompting the user to replace the print unit.
FIG. 12 is a diagram for describing conventional lifespan management information for a component, as stored in a non-volatile memory. In FIG. 12, the non-volatile memory comprises lifespan management regions, namely: a total print number count region (1); a Y color print unit (PU) print number count region (2)-1; an M color PU print number count region (2)-2; a C color PU print number count region (2)-3; a K color PU print number count region (2)-4; a Y color toner cartridge (TC) print number count region (2)-5; an Mcolor TC print number count region (2)-6; a C color TC print number count region (2)-7; a K color TC print number count region (2)-8; a fixing unit print number count region (2)-9; a belt print number count region (2)-10; and a respective color (Y, M, C, K) print position compensation value management region (3).
Each print number count region (2) comprises an upper region and N lower regions. Each of the lower regions is, for example, a region which counts from 0 to 10,000 copies, and when the number of printed copies reaches 10,000, for instance, the count value of the lower region is reset to zero, whilst the count value of the upper region (including a back-up region) is incremented by +1. In other words, the count value of the upper region counts the 10,000 column, for instance. Moreover, the count up to 10,000 copies is performed in any one of the lower regions, and when the count value in that lower region reaches 10,000 copies, the adjacent lower region counts the next 10,000 copies. In this way, each time a count of 10,000 copies is made in one of the lower regions, the lower region performing the count is changed, in a successive fashion. In this way, in a non-volatile memory (EEPROM) which can only provide a rewriteable count value of the order of 10,000, it is possible to perform counts to a higher number than 10,000.
Furthermore, the lifespan copy numbers corresponding to each component are stored in a separate region of the EEPROM or a separate memory (ROM), or the like, and each time the number of printed copies corresponding to each component is counted, it is compared with the respective lifespan copy numbers.
However, by providing a plurality of lower regions, it becomes necessary to provide, for example, approximately several 10 bytes of memory for each print number count region (2). Therefore, since the non-volatile memory of the image forming apparatus comprises respective print number count regions (2) for each of a plurality of components, in total, a memory capacity of approximately several 100 to 1,000 bytes is required. Minimizing the size of the non-volatile memory contained in an image forming apparatus would contribute to achieving cost reduction for the image forming apparatus.